Organic electroluminescent (EL) is a luminous phenomenon of an organic material under the effect of an electric field, of which the electrical energy is directly converted to light energy. In an early time, due to the high driving voltage and low luminous efficiency of the thus prepared device, study on organic electroluminescent devices was at a standstill. Until 1987, Tang et al from the United States Kodak as disclosed in the literature and U.S. Pat. No. 4,356,429 invented a dense and high-quality film by making use of 8-hydroxyquinoline aluminum (Alq3) as the light-emitting material together with an aromatic diamine, and resulted in the formation of an organic electroluminescence device exhibiting high efficiency, low operating voltage, high brightness, and opened a new prologue on organic electroluminescent materials research. However, due to spin-statistical theory, the limit of the theoretical internal quantum efficiency of a fluorescent material is just 25%, since then the way of making full use of the remaining 75% of the phosphorescence to achieve higher efficiency has become a hot research direction in this field. In 1997, Forrest et al discovered the phenomenon of electrophosphorescence, the internal quantum efficiency of the organic electroluminescent material exceeded the 25% limit, which took the research on the organic electroluminescent materials into a new era.
In subsequent studies, the small molecule-doped transition metal complexes such as Iridium, ruthenium, and platinum complexes have become a research focus. The advantage of such complexes lies in achievement of high emission energy obtained from their triplet state. And among them, due to the good stability of the metallic Iridium (III) compounds which allows a mild reaction condition during synthesis, and to their high electroluminescent properties, these compounds has been occupied a dominant position in the subsequent study process. And in order to get a full color display device, generally red-, green- and blue-emitting materials having excellent performance must also be obtained. As compared with the red- and green-emitting materials, the development of blue-emitting material is lagging behind, the improvement of the efficiency and color purity of blue materials has become one of the breakthrough point. To date, Iridium(III)bis[2-(4,6-difluorophenyl)pyridinato-N,C2′](picolinato) (FIrpic) is one of the Ir(III) metal-organic complexes blue electrophosphorescence materials the most frequently reported in the patent literature. Although various optimization have been conducted on FIrpic based OLED structure, and the device performance has also been improved greatly, the biggest weakness of FIrpic is that it emits sky blue, the color purity of blue light is poor, making the CIE of the thus prepared OLED device varying in (0.13 to 0.17, 0.29 to 0.39). Therefore, the development of high-purity blue phosphorescent organic electroluminescent materials has become a major trend in expanding the research work on blue electrophosphorescence materials.